JP5518118B2 - Sealing device for rotating turbine blades - Google Patents

Description

  The present invention relates to an improved sealing device, and in particular to a sealing device supported by or otherwise coupled to a diaphragm ring or diaphragm ring that encloses a radial array of blades or wings. This device can advantageously be used in a turbomachine. The invention particularly relates to an apparatus for preventing fluid leakage through a gap between a rotating part or blade and a turbine casing.

  In the following description, “turbine” is used to refer to a rotating engine having a rotating portion and a stationary portion that are force-coupled by a fluid medium such as water or gas. Of particular relevance to the present invention is an axial turbine having stationary stator blades arranged radially, alternating with a radial array of moving rotor blades. Movement is generally defined as movement relative to the casing or housing.

  A common problem encountered in turbine design and operation is leakage between the rotor blade tips or circumferential shrouds attached to the rotor blades and the housing. Radial turbine operation requires a minimum tip clearance between the rotating blades and the stationary wall of the casing or any extension of the casing. However, this gap creates a leakage flow, which is driven by the differential pressure between the pressure surface and the suction surface.

  In order to reduce tip leakage it is known to close the gap between the rotating part and the fixed part with a suitable seal. The most common type of seal used for this purpose is the labyrinth seal. Labyrinth seals typically have a number of radially extending annular knives provided in one part and corresponding annular seal lands, or arrays of threats or grooves provided in the other part. All types of labyrinth seals have the common feature of providing a tortuous path for fluid through the gap. In order to prevent tip leakage in the turbine, the seal is often in the form of a complete ring that is normally assembled in the casing as a two-part or segment supported by the casing.

  Since labyrinth seals are well known and used in the design of all major turbine manufacturers, for the purposes of the present invention, such seals are complex in shape, which is to function properly. It is enough to emphasize that it must be cut with close tolerances. Any movement of the seal member during operation from the standard position typically increases significantly the leakage or friction between the movable and fixed parts. Known labyrinth seals for rotating blades are integrated into the inner casing of the turbine and the diaphragm structure or ring carrier.

  Some seals are assembled as spring-supported packages to move the seal members relative to each other during radial expansion or contraction of the rotating part. In spring-supported seals, the elastic force presses one part of the seal against the other, thereby preventing gap enlargement or excessive friction. Examples of such solutions are also known. For example, in the AEG document "Spezielle Konstrucktionsaufgaben aus dem AEG-Grossturbinenbau", Hans Reuschke (DK 621.165-181.2: 62.0022) Supporting the seal in between is described.

  Known alternatives to the labyrinth seal are brush seals and finger seals. These types of seals generally have a plurality of flexible members attached to one part that are in sealing engagement with suitable surfaces in the other part.

  Another alternative, which is known but less commonly used, is a film riding seal having two suitable molded engagement surfaces. As the turbine rotates, a thin film of fluid is formed between the surfaces and a small lifting force separates these surfaces. Typically, an elastic element is provided in the seal design to apply a restoring force, which reduces the starting friction and counters the lifting force and provides an appropriate constant gap between the sealing surfaces. maintain.

  In turbine design, when retrofitting existing older turbines with modern and more efficient components, particularly blades, the options for how to install the seal are often limited. In some modifications, it may not be possible or desirable to attach the fixed portion of the seal directly to the turbine casing or otherwise securely couple. The design described in co-owned published U.S. Patent Application Publication No. 2008/0170939, which is hereby incorporated by reference in its entirety, is designed so that the securing portion of the seal is Fig. 4 shows an example to illustrate a seal design that is not tightly coupled to the casing.

  Currently, it has been found that depending on the manner in which the seal is coupled to the turbine stator, the seal may cause displacement or distortion caused by the force on the stator blades as fluid flows through the turbine. ing. This displacement usually creates a wider gap between the sealing surfaces, thereby reducing the sealing performance. Another displacement that leads to an increase in the seal gap may be the result of deformation of the inner casing of the turbine.

US Patent Application Publication No. 2008/0170939

  The object of the present invention is therefore to reduce or eliminate the effects of these displacements or deformations.

  In accordance with one aspect of the present invention, a seal is provided for a turbine having a continuous diaphragm that provides outer support for a radial arrangement of alternating stationary blades, the seal being external to the rotating blades. A radially and axially supported outer seal portion that forms part of a seal that reduces fluid flow around the end, the radial support portion of the outer seal portion comprising a key and a circumferential direction It is formed as a ring that is held in place in the radial direction by the extension, and the key and circumferential extension have sufficient clearance to ensure axial support for the pressure seal surface and casing Allowing relative radial movement between the ring and the casing, the ring having sufficient clearance from the casing and / or diaphragm, Are substantially isolated from the is displaced radially during the rotational movement of the diaphragm (in the axial plane) in direction, that is, so as not to displace in the radial direction.

  An object of the present invention is to provide an outer seal portion for sealing the tip of a rotating blade. The new outer seal portion is designed to be less sensitive to rotational movement of the vane or stationary blade and the diaphragm or casing portion coupled to the vane. This rotational movement may occur when the stationary blade receives a flow force. The present invention has a stabilizing structure that radially supports the outer seal portion. That is, this stabilization structure is formed as a ring inserted into the casing. The ring body has sufficient clearance for the upstream and / or downstream diaphragms. Diaphragm is defined herein to include any base portion of the stationary blade, or the inner extension of the casing itself.

  The ring has an outer circumferential, radially outwardly extending extension or rim, which extends in the axial direction of the turbine engaging the juxtaposed surface or edge of the casing. Provide support for. Alternatively, the circumferential extension can project radially inward from any part connected to the casing, such as a casing or diaphragm. Both options can provide axial support for the ring.

  However, it is important to note that the axial support in the form of keys and circumferential extensions is designed to allow small radial movement of the ring relative to the casing. This isolates the ring from the resulting deformation even if the casing is distorted from the standard shape by flow forces or temperature differences.

  In a first preferred variant of the above aspect of the invention, the axial support is provided by a machined edge or groove provided on the outer periphery of the ring, the axially directed surface being a corresponding groove in the casing. Or contact the juxtaposed surfaces at the edges.

  In a second preferred variant of the above aspect of the invention, the axial support is provided by a machined edge or groove provided in the outer periphery of the ring, which is arranged in the gap between the diaphragm and the casing. .

  It may be advantageous to design the ring-shaped support to have inner and outer rings for ease of installation and maintenance.

  It is possible to further enhance the performance of the seal, for example by elastically attaching the outer sealing surface with a spring. The resilient attachment maintains contact between the seal surfaces even if the gap between the inner seal surface and the outer seal member at the tip of the rotating blade changes.

  These and other aspects of the invention will become apparent from the following detailed description and the drawings listed below.

  Exemplary embodiments of the invention are described below with reference to the accompanying drawings.

FIG. 2 is a partial radial cross-sectional view of two moving turbine blade rows and a fully assembled turbine diaphragm according to the present invention disposed between the moving blade rows. FIG. 6 schematically illustrates the effect of axial rotation of a fixed blade on a supported seal. 1 is a schematic radial cross-sectional view illustrating a first example according to the present invention. FIG. FIG. 6 is a schematic radial cross-sectional view showing a second example according to the present invention. FIG. 6 is an axial sectional view and a radial sectional view showing a third example according to the present invention.

  In the following description, referring first to the so-called “compact diaphragm” design illustrated by FIG. 1, which reproduces the relevant features of FIG. 2 of the above-cited US Patent Application Publication No. 2008/0170939. Details of embodiments and examples are described in further detail. FIG. 1 is a partial radial cross-sectional view showing a fully assembled diaphragm disposed between successive annular rows of moving blades or blades 12, 13 in a steam turbine. Each of the movable blades is provided with T-shaped root portions 14 and 15 on the radially inner side, and these root portions 14 and 15 are provided in corresponding slots 16 and 17 formed on the peripheral surface of the rotor drum 18. Has been placed. A radially outer element called shrouds 19 and 20 is also provided at the tip of the movable blade. In the illustrated example, the shrouds 19 and 20 support the movable part of the labyrinth seal. The surrounding divided rings 21 and 22 support the fixed part of the seal. These rings 21 and 22 are rigidly connected to the upstream and downstream diaphragm rings 33 and 34, and these diaphragm rings 33 and 34 themselves are mounted in the casing 10 of the turbine. As is known, the seal between the shrouds 19, 20 and the rings 21, 22 is achieved by lips or fins 23, 24 that are press fit into grooves machined into the divided rings 21, 22.

  It is important to note that the split rings 21, 22 are supported by diaphragm rings 33, 34, which are welded to the bottom of the stator blades or vanes 30, 31 themselves. .

  During operation, the stator blades 30, 31 are exposed to flow through the turbine. The force transmitted by this flow has various effects on the stationary part of the turbine. 2A and 2B illustrate the effect of a small rotation or bending movement of an axial fixed blade using an example of one blade. One or more of the same elements having the same function in FIGS. 1 and 2 are indicated by the same reference numerals.

  The assembled or standard position of blade 30 and seal support ring 21 is shown in FIG. 2A. FIG. 2B shows the blade 30 being bent in the direction of flow and performing a slight rotational movement including the diaphragm ring 33 and the seal support ring 21. The movement of the support ring 21 is indicated in FIG. 2B by the maximum radial movement x and the rotation angle α. The effect of this deflection on tip leakage depends on the specific geometry and other parameters for a given turbine design, but simulations show that displacement increases tip leakage area by more than 30%. There is a fear. The effect of rotational movement is shown here using the example of a stator blade attached to a diaphragm ring, but not so much when the stator blade is fixed directly to the casing as in other turbine designs. Although not noticeable, a similar effect occurs.

  A first exemplary device for reducing tip leakage due to rotational movement is shown in FIG. Elements of FIG. 3 that have already appeared in the same or similar form in the drawings are again denoted by the same reference numerals. In this example, the seal support ring 21 is a rim-like structure with inwardly bent flanges that provide radial and axial support for the seal element 23. The support ring 21 has a gap between the upstream and downstream diaphragm rings 33 and 34. The support ring 21 is shown screwed at the half joint using bolts 25. The ring 21 is inserted into the casing 10 at a support key 28 and is sealed in the axial direction by a circumferential extension 27 of the ring projecting radially outward. The seal element 23 is supported by an elastic element 29 while being held at a predetermined position in a chamber formed by a flange bent inward of the ring 21, and the elastic element 29 is in contact with the opposing surface. Work to maintain state. The elastic element 29 can include a leaf spring, for example. The facing surface is provided on the tip of the rotating blade 13 or the shroud 19.

  When the casing 10 is deformed in the radial direction, for example by thermal stress, the circumferential extension 27 outside the ring 21 is sufficient in the corresponding circumferential groove 11 of the casing 10 to allow the resulting distortion. Has a radial gap. The clearance between the ring 21 and the diaphragm rings 33, 34 is sufficient to isolate the ring 21 from small axial rotations as detailed in FIG. 2 above.

  A second exemplary apparatus according to the present invention is shown in FIG. Elements of FIG. 4 that have already appeared in the same manner in the above figures are again indicated with the same reference numerals. In this example, the seal support ring 21 is shown having an L-shaped cross section. The outer circumferential edge 27 of the ring 21 extends into the gap between the upstream diaphragm ring 34 and the casing 10. This extended seal support ring 21 in this example is inserted into the casing 10 and bolted at the joint as in the above example. The circumferential notch 26 provides a gap between the (radial) inner seal support portion of the ring 21 and the diaphragm 34 and rotates the diaphragm 34 without causing the ring 21 to follow the radial movement of the diaphragm.

  In a third example as shown in FIGS. 5A and 5B, the support ring is axially engaged by engaging an axially directed surface or edge in the radially inwardly projecting portion 27 of the casing 10. Provides a pressure seal directly at. Since this extended part of the casing is not affected by the rotation of the stator blades 30, 31 or the diaphragm rings 33, 34, the support ring is still isolated from the effect of such rotation. In this example, the support ring is inserted using the key 28 as in the previous example. However, to facilitate this attachment, the support ring 21 of FIG. 5 is divided into inner and outer rings 51, 52, respectively. The inner ring 51 supports the seal 23. The transverse key 53 prevents rotation of the entire ring structure around the central axis of the turbine, whereas the transverse pins 54 and 55 prevent rotation of the inner ring 51. A key such as the lateral key 53 can also be used to secure the ring in the above example.

  The present invention has been described above purely by way of example, and modifications can be made within the scope of the invention. For example, the stator blades can be attached directly to the inner radial extension of the casing rather than to the diaphragm ring. The seal support ring is then separated from such extensions by a gap.

  The invention may be any and all features described or implied herein or shown or implied in the drawings, or any combination of any such features, or equivalents of the invention. Or any generalization of combinations. In other words, the scope of the present invention should not be limited by any of the above exemplary embodiments. Each feature disclosed in the specification, including the drawings, may be replaced by an alternative feature serving the same, equivalent, or similar purpose unless explicitly stated otherwise.

  Unless expressly stated herein, any prior art description in the specification is not an admission that such prior art is widely known or forms part of common general knowledge in the art. Absent.

DESCRIPTION OF SYMBOLS 10 Casing 11 Circumferential groove | channel 12, 13 Movable blade 14,15 Radial inner side T-shaped part 16,17 Corresponding slot 18 Rotor drum 19,20 Shroud 21,22 Seal support ring 28 Support key 23,24 Seal Fin / seal element 25 Bolt 26 Circumferential cutout 27 Radial circumferential extension 29 Elastic element 30, 31 Fixed blade 33, 34 Upstream and downstream diaphragm rings 51, 52 Inner and outer support rings 53 Transverse keys 54, 55 Horizontal pin x Maximum radial movement α Rotation angle

Claims (6)

  In a seal for a turbine having a continuous diaphragm that provides outer support for the radial arrangement of stationary blades alternately arranged in the axial direction, the seal allows fluid flow around the tip of a rotating blade. A ring having a radially and axially supported outer seal portion forming part of a reducing seal, wherein the radial support portion of the outer seal portion is held in place by a key and a circumferential extension. The key and the circumferential extension have a sufficient clearance so that the pressure seal surface and the axial support can be ensured while the casing part and / or the diaphragm and the ring are relative to each other. In such a way that the ring has sufficient clearance from the casing part and / or the diaphragm. Accordingly, characterized in that so as not to displace in the radial direction during the rotational movement of the part and / or the diaphragm of the casing in the axial direction, the seal for the turbine.   The axial support is provided by an extension of the outer periphery of the ring having an axially oriented surface for contacting juxtaposed surfaces in corresponding grooves provided in the casing. The seal described.   The seal of claim 1, wherein the axial support is provided by an extension of the outer periphery of the ring disposed in the gap between the diaphragm and the casing.   The axial support is provided by an extension of the inner circumference of the casing having an axially directed surface for contacting a juxtaposed surface at a corresponding groove or edge of the ring. The seal described.   The seal of claim 1, wherein the ring has an inner ring and an outer ring mounted together in a turbine casing and secured against relative rotation.   The ring includes a radially acting resilient element designed to close a gap between the outer seal portion and a seal portion attached to the tip or shroud of the rotating blade. Item 1. The seal according to item 1.

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